A data-processing system that obtains knowledge useful for business by performing breakdown or analysis of a large amount of data obtained from hour to hour (stream data) in real time is called a Cyber Physical System (CPS) or the like, and needs thereof have been increased.
As a structure of such a data-processing system, a structure in which stream data is firstly stored in a storage device (data store) and the stored data is analyzed by a separate computer is considered. By accumulating the data, a buffer memory on a sensor device side can be released faster. In addition, by accumulating the data, a plurality of computers that perform analysis can also use the data.
The storage device obtains and accumulates stream data, such as a running condition and a position of a vehicle, a position of a user of a mobile terminal, and weather data, from a sensor or a device of a vehicle, a mobile terminal, meteorological equipment and the like. Concurrently, the storage device provides the accumulated stream data for a computer that performs analysis. The computer that performs analysis carries out analytical processing on the stream data accumulated in the storage device depending on a predetermined breakdown scenario to generate a breakdown result. As an example of processing by the computer that performs analysis, there are Complex Event Processing (CEP), MapReduce processing, and the like.
For example, in a monitoring system of traffic information, stream data such as a speed of each vehicle detected by a sensor mounted on each vehicle is accumulated in a storage device. Concurrently, a future position of the vehicle is calculated by a computer that performs analysis, based on the most recent position and speed of each vehicle accumulated in the storage device. Then, presence or absence of occurrence of a traffic jam, an accident, and the like can be detected by checking a future position of each vehicle.
In consideration of scalability of a system in a case that the data volume that should be accumulated is increased, the storage device is considered to be achieved based on a distributed data store structure. FIG. 7 is a diagram illustrating a structure of a distributed storage device 140 based on the distributed data store structure as an example. Referring to FIG. 7, the distributed storage device 140 includes a plurality of storage nodes 110a to 110n connected to one another via an inter-storage network 130. Each of the storage nodes 110a to 110n includes a storage medium, and a calculator capable of being connected to the inter-storage network 130. Further, a control function of a data store can be achieved by distributed processing with the plurality of storage nodes 110a to 110n. 
As a related art, a snapshot that generates a rest point image in a storage is described in NPL 1. Further, a technology for transmitting a consistent still image before an initial access (BEGIN) to a certain client in a database is described in NPL 2.